I don't see them doing it on iOS, but I do wish someone would create a plugin or hack for OS X that would allow it on my MacBook where it's more technologically possible. OS X apps can be resized to any size without problems so a hack would simply need to tell the fullscreen app to resize to a smaller area and somehow allow a second app to also resize to the other smaller area. Though I'd still also like to have certain apps float above the screen on all spaces like a PIP but it hasn't happened yet either.Yeah, as much as I would want something like that (ala Windows 8 side-by-side fullscreen features) I don't think it'll be happening any time soon.
Instead, they'll continue to improve on the multitasking and app switching abilities, like bringing mission control/espose to iOS in some form. That is a more likely prospect, imo.